Maran sex isn't easy. The roos stay hen like for a while. At day old the femail flight feathers are faster growing than the male. The girls will be sprouting wings. Cuckoo marans roos are lighter in color than the girls at birth on. Actually a natural occurring sex link. Coppers at day old ,roos are usually just more robust and larger sometimes with a tell spot of white but not acurate.
At four weeks the wings have caught up but the back feathers on the roos are slow to fill in. The combs at four seeks are usually starting to show male character. After that the rest is cake.GP